The present invention relates to a process for producing a novolak type phenol resin with less unreacted phenol and a narrow molecular weight distribution in high yield. The novolak-type phenol resin produced according to the present invention is used as a suitable binder for molding materials, friction materials, grinding materials, sealants, etc.
Heretofore, a novolak-type phenol resin has been obtained by reaction of a phenol with an aldehyde, using an inorganic or organic acid such as hydrochloric acid, sulfuric acid, phosphoric acid, phosphorous acid, oxalic acid, p-toluenesulfonic acid, etc. as a catalyst. A novolak-type phenol resin can be adjusted in the molecular weight generally by changing a charge ratio of a phenol to an aldehyde, etc. but has a broader molecular weight distribution. The ordinary means for narrowing the molecular weight distribution includes a method of conducting the reaction in an organic solvent and a method of removing low-molecular weight components by steam distillation or solvent washing. In the case of the former method, no low-molecular weight novolak-type phenol resin can be obtained, whereas in the case of the latter method, the yield is considerably lowered.
An object of the present invention is to produce a novolak-type phenol resin with less unreacted phenols and a narrow molecular weight distribution in high yield.